188 ANNUAL OF SCIENTIFIC DISCOVERY. 



supplied for drinking purposes, but are content with showing that 

 it is as transparent and colorless as ordinary river water; that it 

 can be taken into the mouth, and even drank, without repug- 

 nance ; that fishes can live in it ; and, most important of all, that 

 it is not only free from any offensive smell, but that it may be 

 kept for months, and a sample has actually been kept through the 

 entire hot summer of this year, without showing any tendency to 

 putrefy, or emit any disagreeable odor. So that, for the above 

 reasons, we believe that the affluent water from the phosphate 

 process may be allowed to flow directly into the rivers, without 

 injury either to the fish in them, or to the health of the inhabitants 

 on their banks. 



" Coming now to the second question, I would premise by stating 

 that I believe the agricultural value of sewage lias, in general, 

 been much over-estimated. That the excreta may have originally 

 represented a value of -from 8 to 20 shillings per head, as esti- 

 mated by various writers, is not improbable ; but it is as incor- 

 rect to regard the sewage as representing the same value as the 

 original excreta, as, for example, to assert that the water in a 

 barrel, into which a bottle of brandy worth 5 shillings has been 

 poured, is equal in value to the original brandy ; the whole of 

 the brandy could be recovered by distillation, but probably at a 

 cost greater than its value ; and this would also be the case with 

 sewage, if we attempt to extract the entire manurial contents. 



"Chemists are all agreed that no chemical combinations are 

 known by which the whole of the sewage contents, valuable for 

 agriculture, can be precipitated ; and in our attempts, fully recog- 

 nizing this, we have only endeavored to extract so much as will 

 leave the affluent water in a condition sufficiently pure as to be 

 innoxious. In regard to the ammonia, the phosphate process 

 converts it into its most insoluble known compound, the 

 double phosphate of ammonium, and magnesium; and the extent 

 to which it is recovered, is dependent upon the length of time al- 

 lowed for subsidence, and the solvent action of the water, whilst 

 experiments made with London sewage show that the purified 

 sewage retains but a mere trace of organic matter. A most im- 

 portant feature of the phosphate process, however, one in 

 which it differs from all those previously proposed, is the fact 

 that the substances employed in the purification are only such as 

 really augment greatly the agricultural value of the precipitated 

 manure, and thus make it sufficiently valuable to bear the cost 

 of transport to a distance. The solid deposit from sewage, when 

 considered as a manure, is admitted to be but of extremely little 

 value, and other processes in use, by employing clay or other 

 worthless substances, diminish the value of the resulting ma- 

 nure to such an extent that it is utterly worthless except in the 

 immediate vicinity of the works. On the other hand, in the new 

 process, what is added are compounds rich in phosphoric acid in 

 a state of combination available for immediate assimilation by 

 the plants themselves. 



" The natural phosphate of aluminum, which we specially recom- 

 mend, is a product which at present has no commercial value, 



